PURPOSE: The purpose of this study is to determine in subjects with type 1 diabetes mellitus: whether glycemic control can be achieved at least as effectively with an insulin regimen involving pre-meal inhaled insulin plus a single bedtime Ultralente injection as with a conventional subcutaneous insulin regimen involving 2-3 injections per day; and the toleration and safety of inhaled insulin therapy and its effect(s), if any, on measures of pulmonary function. METHODS: This is an open-label, 3-month, parallel, multicenter study. A total of 60 subjects (a total for all sites) with type 1 diabetes will be evaluated in this study. Subjects who successfully complete the 3-month comparative trial will be eligible to receive inhaled insulin in a one- year, open-label protocol extension. In the comparative trial the control condition is insulin injection therapy, given either BID or TID, depending upon the subject's usual (prestudy) administration regimen. For subjects randomized to the control group, insulin doses will be adjusted to optimize control based on glucose monitoring results, but the prescribed frequency of dosing will not change from the subject's usual BID or TID schedule. In the one-year extension, patients may elect to return to subcutaneous insulin or to continue or start inhaled insulin. As in the 3-month trial, subcutaneous insulin adjustments will be based on glucose monitoring results, and the prescribed frequency of dosing will not change from the subject's usual BID or TID schedule.